The present invention relates to a semiconductor device and an optical pickup device used for optical information processing, optical measurement, optical communication and the like.
A conventionally known semiconductor device integrated with two light sources has either a hybrid integration in which a red semiconductor laser element and an infrared semiconductor laser element are arranged independently inside an optical-pickup or a monolithic integration in which a red semiconductor laser structure and an infrared semiconductor laser structure are integrated on the same substrate.
These two examples of integration will be described below.
First, a conventional semiconductor device with a monolithic integration of two light sources will be described schematically by referring to FIG. 14.
As shown in FIG. 14, in this semiconductor device 1, on top of a photodiode IC 2, a semiconductor laser element 3 emitting a laser beam L11 having a wavelength of about 650 nm, for example, used for DVD, a semiconductor laser element 4 emitting a laser beam L12 having a wavelength of about 780 nm, for example, used for CD, a photodetector 5 having a plurality of sensor elements 5a to 5d and a micro-prism 6 functioning as a reflecting mirror are integrated. Furthermore, on the upper side of the micro-prism 6, a hologram plate 7 is disposed for dividing a light beam returning from an optical recording medium (not shown) such as an optical disc into the zero-order light, the + first-order light, and the xe2x88x92 first-order light and allowing them to enter the sensor elements 5a to 5d (See JP11 (1999)-149652A). In addition, as for the semiconductor laser elements 3, 4, those formed on the same LOP 8 are known (Nikkei Electronics, the Jun. 28, 1999 Issue, pages 29 to 30).
Next, a conventional semiconductor device with a hybrid integration of two light sources will be described schematically by referring to FIG. 15.
As shown in FIG. 15, in this semiconductor device 9, on top of a substrate 10, a semiconductor laser element 11 emitting a laser beam L13 having a wavelength of about 650 nm, for example, used for DVD, a semiconductor laser element 12 emitting a laser beam L14 having a wavelength of about 780 nm, for example, used for CD, a plurality of photodetectors 13, 14 and a micro-prism 15 functioning as a reflecting mirror are integrated. Moreover, on the upper side of the micro-prism 15, an optical element (not shown) is disposed for allowing light beams L13xe2x80x2, L14xe2x80x2 returning from an optical recording medium (not shown) such as an optical disc to enter the photodetector 13, 14 (See JP9 (1997)-120568A, JP10(1998)-64107A, JP11 (1999)-39693A, JP11 (1999)-161993A). In addition, the semiconductor laser elements 11, 12 are mounted respectively on the substrate 10 via mounts 17, 18.
However, the conventional configurations described above had the following problems.
First, with regard to the conventional semiconductor device with a monolithic integration of two light sources, the semiconductor laser element 3 and the semiconductor laser element 4 are arranged next to each other in such a manner that the emitting end faces of the lasers are facing the same direction. Therefore, it was difficult to reduce the interval between the emission points of the semiconductor laser element 3 and the semiconductor laser element 4 to 100 xcexcm or less. As a result, the red laser and the infrared laser respectively emitted from the two semiconductor laser elements 3, 4 were affected differently from the optical element, so that one of the semiconductor laser elements suffered from deterioration of its operating characteristics. In particular, when the semiconductor laser element 3 and the semiconductor laser element 4 are arranged close to each other and one of the two semiconductor laser elements 3, 4 is operated with a high power of 30 mW or higher, heat generated in one of the semiconductor laser elements affects the other semiconductor laser element, which causes the characteristics of the semiconductor laser elements to deteriorate.
Furthermore, with regard to the conventional semiconductor device with a hybrid integration of two light sources, the micro-prism 15 is arranged between the semiconductor laser element 11 and the semiconductor laser element 12. Therefore, when the location of the micro-prism 15 is shifted from. the predetermined position, the optical paths of the laser beams L13, L14 emitted from the semiconductor laser elements 11, 12 respectively are shifted. As a result, according to this amount of shifting, an apparent interval between the emission points of the semiconductor laser element 11 and the semiconductor laser element 12 (hereinafter, reference to xe2x80x9cinterval of emission pointsxe2x80x9d includes xe2x80x9capparent interval of emission pointsxe2x80x9d) varied, which made it difficult to reduce the interval of the emission points.
Moreover, the conventional semiconductor device described above is configured such that the semiconductor laser elements are mounted via a mount such as the LOP 8, so that the interval of the emission points varied according to the uneven thickness of the mount, which made it difficult to reduce the interval of the emission points.
It is an object of the present invention to solve the conventional problems described above by providing a semiconductor device and an optical pickup device, which are capable of reducing an interval of emission points between a plurality of semiconductor laser elements and also capable of preventing heat generated when a semiconductor laser element is operated with a high power from affecting other semiconductor elements.
To achieve the above object, a configuration of a semiconductor device of the present invention includes a substrate, a protrusion having a plurality of side faces formed on the substrate by processing the substrate, and a plurality of semiconductor laser elements disposed on the substrate, wherein the plurality of semiconductor laser elements is arranged such that each end face thereof is opposed to a different side face of the protrusion. According to the configuration of this semiconductor device, the protrusion having a plurality of side faces is formed on the substrate, so that a micro-prism is no longer necessary. Furthermore, the plurality of semiconductor laser elements can be arranged on a straight line, so that an interval of emission points between the plurality of semiconductor laser elements can be reduced. In addition, since the plurality of semiconductor laser elements is arranged such that each end face thereof is opposed to a different side face of the protrusion, heat generated when a semiconductor laser element is operated with a high power can be prevented from affecting other semiconductor elements. As a result, it is possible to prevent the characteristics of the semiconductor laser elements from deteriorating.
Furthermore, in the configuration of the semiconductor device of the present invention, it is preferable that the protrusion is formed into a truncated pyramidal shape, and that a photodetector is disposed on a top face of the protrusion. According to this preferred configuration, the photodetector can be positioned in one place, so that the semiconductor device can be miniaturized.
Moreover, in the configuration of the semiconductor device of the present invention, it is preferable that the semiconductor device further includes a plurality of small protrusions formed on the substrate by processing the substrate, and that a semiconductor laser element is mounted on each of the small protrusions. According to this preferred configuration, particularly when the semiconductor laser elements are mounted p-side down, it is possible to prevent a part of the laser beams emitted from the end faces of the semiconductor laser elements from being blocked by the surface of the substrate.
Furthermore, in the configuration of the semiconductor device of the present invention, it is preferable that a groove is formed between the semiconductor laser element and the side face of the protrusion on the substrate. According to this preferred configuration, it is possible to prevent a part of the laser beams emitted from the end faces of the semiconductor laser elements from being blocked by the surface of the substrate.
Moreover, in the configuration of the semiconductor device of the present invention, it is preferable that the protrusion has four side faces having an angle between 40xc2x0 and 50xc2x0 with respect to a principal plane of the substrate, and that the semiconductor laser elements are arranged such that emitting end faces for main beams are opposed to the side faces of the protrusion. According to this preferred configuration, the main beams emitted from the semiconductor laser elements can be reflected at the side faces of the protrusion and move in the direction perpendicular to the substrate.
Furthermore, in the configuration of the semiconductor device of the present invention, it is preferable that the substrate is a silicon substrate, and that the principal plane of the substrate is a (1 0 0) plane inclined at an angle in the range between 5xc2x0 and 15xc2x0 in a  less than 1 {overscore (1)} 0 greater than  direction, and that one of the side faces of the protrusion opposed to the emitting end faces for the main beams of the semiconductor laser elements is a (1 1 1) plane. According to this preferred configuration, it is possible to make the incident angle formed by the main beam of the semiconductor laser element with the side face of the protrusion become closer to 45xc2x0.
Moreover, in the configuration of the semiconductor device of the present invention, it is preferable that the substrate is a silicon substrate, and that the principal plane of the substrate is a (5 1 1) plane inclined at an angle in the range between 1xc2x0 and 11xc2x0 in a  less than 1 {overscore (1)} 0 greater than  direction, and that one of the side faces of the protrusion opposed to the emitting end faces for the main beams of the semiconductor laser elements is a (1 1 1) plane. According to this preferred configuration, it is possible to make the incident angle formed by the main beam of the semiconductor laser element with the side face of the protrusion become closer to 45xc2x0.
Furthermore, in the configuration of the semiconductor device of the present invention, it is preferable that the semiconductor device further includes a concave portion having a plurality of side faces formed on the substrate by processing the substrate, and that the protrusion and the plurality of semiconductor laser elements are disposed inside the concave portion. Furthermore, in this case, it is preferable that the plurality of semiconductor laser elements is arranged such that each end face on the opposite side of the end faces opposed to the side faces of the protrusion is opposed to a different side face of the concave portion. In this case, furthermore, it is preferable that a main beam is emitted from one end face of the semiconductor laser element and a monitor light beam is emitted from the other end face thereof, and that a monitoring photodetector for receiving the monitor light beam is provided on the side face of the protrusion or the side face of the concave portion opposed to the emitting end face for the monitor light beam. According to this preferred configuration, the power of the main beam emitted from the semiconductor laser element can be controlled. Furthermore, in this case, it is preferable that the photodetector is disposed on the periphery of the concave portion. According to this preferred configuration, a plurality of photodetectors can be arranged, so that the light-receiving sensitivity of the semiconductor device can be improved. In this case, moreover, it is preferable that the photodetector has light-receiving areas divided into a plurality of portions. According to this preferred configuration, by carrying out the calculation of signals in the plurality of divided light-receiving areas, a tracking error detection can be performed with high accuracy. Moreover, in this case, the photodetector is divided in the direction parallel to the end face of the semiconductor laser element. According to this preferred configuration, even if the positions of the semiconductor laser elements are shifted from the predetermined positions, it is possible to have the quantity of the return light beams entering the photodetector scarcely change. Moreover, in this case, it is preferable that a groove is formed between the semiconductor laser element and the side face of the concave portion on the substrate. Also, in this case, it is preferable that the substrate is a silicon substrate, and that a bottom face of the concave portion is a (1 0 0) plane inclined at an angle in the range between 5xc2x0 and 15xc2x0 in a  less than 1 {overscore (1)} 0 greater than  direction, and that one of the side faces of the concave portion opposed to the emitting end faces of the main beams of the semiconductor laser elements is a (1 1 1) plane. Furthermore, in this case, it is preferable that the substrate is a silicon substrate, and that a bottom face of the concave portion is a (5 1 1) plane inclined at an angle in the range between 1xc2x0 and 11xc2x0 in a  less than 1 {overscore (1)} 0 greater than  direction, and that one of the side faces of the concave portion opposed to the emitting end faces for the main beams of the semiconductor laser elements is a (1 1 1) plane.
Furthermore, a first configuration of an optical pickup device of the present invention is characterized in that a plurality of semiconductor laser elements, a plurality of photodetectors and a plurality of reflecting surfaces are disposed on the same substrate, and each of the semiconductor laser elements further includes a semiconductor device arranged such that each end face thereof is opposed to a different reflecting surfaces and a hologram element is positioned along an optical axis of a light beam emitted from the semiconductor laser element toward an optical recording medium. According to the first configuration of the optical pickup device of the present invention, the semiconductor device itself can be miniaturized, so that the miniaturization of the optical pickup device can be achieved.
Moreover, a second configuration of an optical pickup device of the present invention includes a semiconductor device having a plurality of semiconductor laser elements and a hologram element positioned along an optical axis of a light beam emitted from the semiconductor laser elements toward an optical recording medium, wherein the semiconductor device of the present invention is used as the semiconductor device.
Furthermore, in the first or the second configurations of the optical pickup device of the present invention, it is preferable that the hologram element has a plurality of diffraction gratings. According to this preferred configuration, the return light beams from the optical recording medium originated from each of the plurality of semiconductor laser elements can be made to enter each of the plurality of photodetectors.